176 Regeneration 



will be pulled nearer d. In this way purely mechanical 

 conditions are responsible for the fact that the soft 

 tissues of the animal are gradually restored to their 

 true orientation. 



As a final possible example of the influence of internal 

 secretion or substances contained in the blood may 

 be mentioned the following curious observation of 

 Przibram.' In a crustacean, Alpheus, the two chelas 

 (pincers) are not equal in size and form, one being 

 very much larger than the other. Przibram found that 

 when he cut off the larger pincer in such crustacean? 

 the remaining pincer assumes in the next moulting 

 the size and shape of the removed large pincer; while 

 in place of the removed pincer one of the small type 

 is produced. Hence a reversal of the two pincers is 

 thus brought about. If later on the large pincer is 

 again cut off the process is repeated and the original 

 dissymmetry is restored. Przibram was able to show 

 that the nervous system has no connection with this 

 phenomenon. 



The elements which have entered into the discussion 

 thus far are, first, the flow of substances in preformed 

 channels; second, the existence of general or specific 

 substances required for the growing or regenerating 

 organ. A third element is to be added; namely the 

 *' suction" effect upon these substances of a developing 

 organ. Thus we see that if one or a few of the notches 



'Przibram, H., Arch.f. Entwcklngsmech., 1901, xi., 329. 



